Process for making synthetic paper yarn



United States Patent 01 ice 3,212,251 Patented Oct. 19, 1965 3,212,251PROCESS FOR MAKING SYNTHETIC PAPER YARN William Finan Linke and WalterFlorus Reynolds, Stamford, Conn, assignors to American Cyanamid Company,Stamford, Conn., a corporation of Maine No Drawing. Original applicationNov. 27, 1962, Ser. No. 240,428, now Patent No. 3,168,802, dated Feb. 9,1965. Divided andthis application Apr. 7, 1964, Ser. No. 358,106

5 Claims. (Cl. 57-157) This is a division of application Serial No.240,428, filed by us on November 27, 1962, now Patent No. 3,- 168,802,issued February 9, 1965.

The present invention relates to a process for the manufacture oftextile yarn substantially composed of fibrillated polyacrylonitrilepapermaking fibers.

It is known that synthetic paper of unique properties can be prepared byrefining an aqueous suspension of said spun polyacrylonitrile filaments,sheeting the resulting suspension of fibrillated filaments to form awaterlaid web, and drying the web at elevated temperature thereby alsoheat-bonding the fibrils cf. Wooding et al. US. Patent No. 2,810,646(1957). The fibers may be composed of substantially purepolyacrylonitrile, or of a copolymer of acrylonitrile with a minoramount of monomeric material copolymerizable therewith, or of a blend ofa major amount of such polymer or copolymers and a minor amount of adifferent polymer which is COIl'lpatible therewith (of. Belgian PatentNo. 588,577).

At the present time, textile yarn is commercially manufactured bya'method which involves continuously twisting a ribbon of cellulosepaper to the extent of 5 to or more times per inch so as to form a yarnhaving a diameter A or less of the width of the ribbon. The number oftwists per inch is at least sufficient to form the ribbon into a closedhelix but is insuflicient to cause the closed helix to kink. Theresulting yarn is necessarily smooth. A twisting rate of 300 twists perminute is currently regarded as slow, and modern high-speed machinesproduce more than 3,000 twists per minute. Even slow twisting subjectsthe paper to deformation which is sufficiently sudden and sharp to causethe paper to crack. It is necessary, therefore, for the paper to be inlimp state during the twisting step, and this is etfected by pre-wettingthe paper with water.

Water is seriously detrimental to the tensile strength of cellulosepaper, and therefore only wet strength paper (paper which contains a wetstrength resin) is adapted to the twisting process.

Up to the present it has not proved practical to produce yarn fromwater-laid polyacrylonitrile paper because polyacrylonitrile paperpossesses the snap and rattle of crisp bond cellulose paper, and nomeans has been found for rendering the paper limp'without also renderingit tacky, as for example when the paper is sprayed with a solvent.Polyacrylonitrile paper can be wet with water, but the water does notrender the paper sufliciently limp to permit it to be twisted asdescribed.

In the past, it has proved possible to form yarn from polyacrylonitrilepaper ribbon without cracking the ribbon, by twisting the ribbon at veryslow speeds, i.e., at speeds less than about 150 twists per minute.However, the resulting yarn has not proved satisfactory becausepolyacrylonitrile paper is springy, and the resulting yarn possesses astrong intrinsic tendency to untwist. This tendency becomes evident whenthe yarn breaks or is cut, in which event it instantly reverts back topaper ribbon form.

The discovery has now been made that a continuous twisted yarn which hasno inherent tendency to revert to ribbon form can be manufactured atcommercial speed, i.e. at speeds in excess of 300 twists per minute,from a paper ribbon substantially composed of heat-bonded, fibrillatedwater-laid polyacrylonitrile papermaking fibers, without crackingprovided that the twisting is performed while the ribbon is at atemperature in excess of its rattle point. A feature of the invention isthat the resulting yarn, at room temperature, is heat-set, and possessesno tendency to revert back to ribbon form even when broken or cut, and afurther feature is that the process can be performed at high speeds. Wehave successfully produced yarn from polyacrylonitrile paper ribbon atthe rate of 3960 twists per minute, which indicates that the process canbe successfully performed at the maximum rate which modern twistingmachines are capable of.

The product is a continuous smooth, unkinked helical textile yarnconsisting essentially of a heat-set twisted paper ribbon of heat-bondedfibrillated water-laid polyacrylonitrile papermaking fibers.

The invention results from the discovery that when polyacrylonitrilepaper is heated momentarily above its rattle point, the fiber-to-fiberbonds of the paper remain sufiiciently strong to permit the paper towithstand the tensions involved in the twisting operation, and that thisheating does not cause significant permanent detriment to the paper.

As stated, polyacrylonitrile paper normally (i.e., when dry and at roomtemperature) exhibits the rattle and snap characteristic of good qualitybond paper. We have found that when heated, however, the paper passesthrough a transition point above which the paper is substantially aslimp as untreated cloth or wet chamoi-s leather and does not rattle whenshaken. This transition temperature (hereinafter termed the rattlepoint) can be determined by'placirig a sheet of the paper in contactwith an electric hot plate having a known surface temperature, allowingthe sheet to come to thermo-equilibrium, and then rapidly removing thesheet with tongs applied to one corner or end and causing the papersheet to undergo wave-like shakes by rapidly moving the tongs to and frohorizontally while the .paper is suspended vertically. When the test isrepeated over a series of temperatures, the approximate transitiontemperature or rattle point can be readily determined.

The rattle point of most polyacrylonitrile papers appears to be in therange of about -250 F. The paper may be satisfactorily twisted betweenthat temperature and the temperature at which it starts to yellow orbecome tacky, which is generally about 400-550 F. In practice, we preferthat the paper be twisted at a temperature close to but safely above itsrattle point as this temperature (e.g. 50100 F. above the rattle point)does not harm the ribbon and avoid-s the danger of the ribbon breakingwhile it is twisted or of yellowing or becoming tacky.

During yarn manufacture this is most conveniently determined by shakingthe ribbon by hand as it emerges from the heating means. The limpnesswhich the paper possesses above its rattle point is readily perceivedwith a little practice.

We have noticed that a comparatively soft yarn is generally producedwhen the paper is twisted at low temperature (e.g. 150250 F.) and that astronger but harsher yarn is generally obtained when the paper istwisted at a higher temperature, e.g. 300-400 F. The two ranges thusproduce distinct types of yarn.

The invention does not depend on the method employed for heating thepaper ribbon to bring it above its rattle point, and any convenientmethod may be employed. One suitable method is to subject the ribbon todirect infra-red radiation. Another method is to employ a gas flame asthe direct source of heat. Still another means is to heat the ribbon bydirect contact with steam.

In practice, we have found it most convenient to employ a smoothelectrically-heated quartz tube as the heating means, a thermocouplebeing used to determine the temperature within, and a transformer beingprovided so that the temperature may be varied as desired. The ribbon ispassed through the tube, and the temperature of the tube is correlatedwith the speed of travel of the ribbon so that the temperature of theribbon is sufficiently high to ensure that it arrives at the twistingpoint at a temperature safely above its rattle point.

The resulting yarn or thread may be wound at once, and special coolinghas not been found necessary. Thus the yarn may be spooled at atemperature between its rattle point and its tack point.

The yarn produced by the process may contain some or all of thecomponents normally found in synthetic polyaerylonitrile paper as, forexample, wet-strength resins, sizing agents, and pigments and dyes,together with minor amounts of other fibers which may be cellulosepa-permaking fibers.

The yarn has the open, porous, fibrous structure characteristic ofcotton yarn. It may be woven or knitted in normal manner to form textilefabrics. These textile fabrics, being substantially composed ofpolyaerylonitrile fibers, possess particular utility for applicationswhere resistance to water, most organic solvents, ultraviolet light, andacids are desired. These textiles are therefore particularly suited forthe manufacture of chemical filter cloth and outdoor apparatuscoverings.

The invention does not depend upon the number of turns given the ribbonduring the twisting operation. In general the ribbon is twisted so as toprovide a yarn having a diameter or less of the width of the ribbonemployed.

The invention will be more particularly illustrated by the exampleswhich follow. These examples represent embodiments of the invention andare not to be construed as limitations thereof.

Example 1 The paper used was a water-laid web substantially composed ofheat-bonded fibrillated polyaerylonitrile papermaking fibers composed ofapproximately 90% by weight acrylonitrile-10% methylmethacrylatecopolymer. The paper had a basis weight of 35 lbs. per in. per 24" x36"/500 ream, and was supplied as rolls of ribbon in. wide. This ribbonconsistently broke when twisted to the extent of 3 twists per inch atthe rate of 180 twists per minute (ribbon speed 5 feet per minute), butcould be twisted without breaking at 120 twists per minute.

The twisting machine used was a Meadows full-scale 12spindle paperribbon twister, but only one spindle was used.

The machine was modified by installing two quartz heating tubes each 6"long and in diameter for heating the paper ribbon before twisting. Onetube extended upstream from the last steel roller yarn guide locatedapproximately 8 inches from the twisting point, and the other extendeddownstream from this roller guide to the pigtail yarn guide, so thatmost of the twisting occurred while the paper was passing through thelatter tube. Both tubes were wound with nichrome electrical resistancetape and were covered with asbestos paper for thermal insulation. Aninfra-red lamp was positioned above the steel roller guide, over thespace between the tubes, to prevent the ribbon from cooling as it passedthis point.

Electric current was supplied to each of the heating tubes through avariable transformer, and the -trans-- formers were gradually turned upto develop an air temperature estimated at 300 F. within the tubes. Theribbon was run through the heated tubes without being threaded throughthe traveller of a ring and traveller twister, so that no twistingoccurred. As the temperature of the heating tubes increased, atemperature was reached at which the ribbon left the second ordownstream tube in limp state, showing that it was above its rattlepoint. At this point the ribbon was threaded through the traveller andonto the collecting spool. Additional heat was then supplied to ensure atwisting temperature safely in excess of the rattle point of the ribbon,and the twisting machine was placed in full operation at the rate of3,600 twists per minute (ribbon speed 30 feet per minute; 10 twists perinch).

Yarn formation took place smoothly and without difficulty. The paperribbon showed no tendency to break. The temperature of the ribbon at thepoint of twisting was estimated to be approximately 250 F.

The temperature of the heating tubes was varied on either side of thestarting temperature. The ribbon developed a tendency to crack whentwisted at a temperature below approximately 200 F. and the ribbontended to yellow and become tacky when heated above about 500-600 F. Therange 200 F. to 400 F. appeared to be preferable, because verysatisfactory results were obtained without any noticeable change in thecolor or other properties of the fibers.

Example 2 The foregoing procedure was repeated, except that the upstreamheating tube and infra-red lamp were removed, and the downstream heatingtube was replaced by a heating tube 3" in length so as to provide flashheating at a point directly adjacent to the point of twisting. Theresulting yarn had a softer hand than the yarn of Example 1.

Example 3 The procedure of Example 1 was repeated except that theheating tubes and the infra-red lamp were removed, and the ribbon waspassed between two elongated orifices which supplied steam over a 6"length of the ribbon as close to the twisting point as possible, "and aninfra-red lamp was positioned to shine on the ribbon as it advanced tothe twisting point, so as to prevent the ribbon from cooling prior tobeing twisted. Substantially the same results were obtained.

The paper produced by the process of the present application is claimedin the parent application identified above.

We claim:

1. A process for the manufacture of continuous yarn from a paper ribbonsubstantially composed of heatbonded fibrillated water-laidpolyaerylonitrile papermaking fibers, which ribbon cracks when twistedinto a continuous smooth unkinked helical warn at a rate in excess ofabout twists per minute, which comprises continuously twisting saidribbon at a rate in excess of 300 twists per minute to form a continuoussmooth, unkinked helical yarn having a diameter less than about thewidth of said ribbon while said ribbon has a temperature between itsrattle and tack points thereby preventing cracking of said ribbon duringsaid twisting.

2. A process according to claim 1 wherein the ribbon is twisted at atemperature in the range of 50-100 F. above its rattle point.

3. A process according to claim 1 wherein the ribbon is twisted while ata temperature in the range of 300 F. 400 F.

4. A process for the high-speed manufacture of continuous yarn from apaper ribbon substantially composed of fibrillated water-laidpolyaerylonitrile papermaking fibers, which ribbon cracks when twistedinto a continuous smooth unkinked helical yarn at a rate in excess ofabout 150 twists per minute, which comprises continuously twisting saidribbon at a rate in excess of 3,500 twists per minute to form acontinuous smooth, unkinked helical yarn having "a diameter less thanabout the width of said ribbon and flash-heating said ribbon immediatelyprior to said twisting whereby said ribbon is twisted while at atemperature between its rattle and tack points thereby preventingcracking of said ribbon during said twisting 5. A process for thehigh-speed manufacture of continuous yarn from a paper ribbonsubstantially composed of fibrillated water-laid polyacrylonitrilepapermaking fibers, which ribbon cracks when twisted into a continuoussmooth unkinked helical yarn at a rate in excess of about 150 twists perminute, which comprises continuously twisting said ribbon 'at a rate inexcess of 3,500 twists per minute to form a continuous smooth, unkinkedhelical yarn having a diameter less than about the width of said ribbon,flash-heating said ribbon immediately prior to said twisting wherebysaid ribbon is twisted while at a temperature between its rattle andtack points, thereby preventing cracking of said ribbon during saidtwisting and spooling said yarn while said yarn has a temperaturebetween the rattle point and tack point of said paper.

References Cited by the Examiner UNITED STATES PATENTS 1/55 Keeler19-150 4/57 Crouzet 571 14 X 10/57 Wooding .923 12/57 Strang 57-588912/59 Faircloth 57167 2/ 61 Wilke et 'al 57-164 X 7/62 Holmes et al162157 FOREIGN PATENTS 9/20 Germany.

MERVIN STEIN, Primary Examiner.

1. A PROCESS FOR THE MANUFACTURE OF CONTINUOUS YARN FROM A PAPER RIBBONSUBSTANTIALLY COMPOSED OF HEATBONDED FIBRILLATED WATER-LAIDPOLYACRYLONITRILE PAPERMAKING FIBERS, WHICH RIBBON CRACKS WHEN TWISTEDINTO A CONTINUOUS SMOOTH UNKINKED HELICAL WARN AT A RATE IN EXCESS OFABOUT 150 TWISTS PER MINUTE, WHICH COMPRISES CONTINUOUSLY TWISTING SAIDRIBBON AT A RATE IN EXCESS OF 300 TWISTS PER MINUTE TO FORM A CONTINUOUSSMOOTH, UNKINKED HELICAL YARN HAVING A DIAMETER LESS THAN ABOUT 1/10 THEWIDTH OF SAID RIBBON WHILE SAID RIBBON HAS A TEMPERATURE BETWEEN ITSRATTLE AND TACK POINTS THEREBY PREVENTING CRACKING OF SAID RIBBON DURINGSAID TWISTING.